Radio receiving apparatus



Dec. 5, 1933. w PLACE 1,937,784

RADIO RECEIVING APPARATUS Filea Oct. 2, 1931 2 Sheets-Sheet 1 1E V1 I \K 5 .I l II I INVENTOR. VV. 7. 7 /01 a e BY Clam/ 415 Ma ATTORNEY Dec. 5, 1933. w p PLACE 1,937,784

RADIO RECEIVING APPARATUS Filed Oct. 2, 1931 2 Sheets-Sheet 2 nf|| w l- I I I INVENTORI 14 p/aca, BYQ/RW A ATTORNEY Patented Dec. 5, 1933 1,937,784 RADIO RECEIVING APPARATUS Willard P. Place, Wilkinsbnrg, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa, a corporation of Pennsylvania Applicatien ctober2, 1931. Serial No. 566,407

Claims. (Cl. 250

My present invention relates to the art of radio reception and comprises an improved circuit for radio receivers. The new circuit, which includes as a detector a metal oxide rectifier,

:5 lends itself readily to automatic volume control,

results in greater purity of tone with less distortiori and permits of one or more stages of radio amplification succeeding detection. Moreover the essential parts of the new circuit may be ar- 1 0 ranged in the form of an adapter to be included in an ordinary receiving circuit by insertion into the socket of the detector tube; the tube being then plugged into a socket of the adapter.

The use of ,a metal oxide rectifier instead of l5 a tube detector in radio receivers is of particular value in eliminating the distortion ordinarily introduced by the tube type of detector due to the transmission thereby of the second harmonic of the modulation frequency. The present in- 20 vention makes possible the substitution of metal oxide rectifiers for tube detectors in radioreceivers with the minimum number of changes in the usual receiving circuit and with resulting improved operation over a wide range of radio fre- V quencies.

. For. an understanding of the invention, reference may be had to the accompanying drawings, ofivhich Fig. 1 is a diagrammatic view of a receiving circuit embodying the invention and utilizing a half wave metal oxide rectifier. Fig. 2

is a diagrammatic view of a receiving circuit similar tothat of Fig. lbut including automatic volume control of the tube preceding the reciher and automaticadjustment of the negative grid bias of the tube succeeding the rectifier. Fig. 3 is a diagrammatic view of a circuit including an adapter forinserting themetal oxide-rectifier into the usual receiving circuit. Figs. 4

and 5 are diagrammatic views illustrating circuits 40 arranged for full wave rectification and not requiring audio frequency amplification asgenerallyunderstood.

Referring to Fig. 1, a metal oxide rectifier comprising the elements la and 1b is connectedacross the secondary of a transformer 2 the primary of which is connected in the output circuit of the preceding. tube 3 of the circuit. The control grid of the succeeding tube 4 is connected intermediate the elements la and lb and the cathode of tube 4 is connected through a. C battery 5 with the grounded input side of element lb. The

circuit is tuned by a variable capacity 6 connected across the secondary of transformer 2. A

source of potential for the plates of tubes 3 and 4 is indicated at 7, input terminals qr tube ,3,

half cycle of the input wave. Thus the rectiat 8 and output terminals for the circuit at 9.

With the above described circuit the effective resistance of the rectifier across the tuned circuit is so high that there is no material increase in the decrement. The inherent capacity of the rectifier, other thanrequiring a change in the setting of capacity 6, has no appreciable effect upon the circuit. As the input'side of element 1b is grounded, the rectifier will maintain the voltage impressed upon the grid of tube 4 constant during one-half of the cycle when alternating current is impressed upon the transformer 2 by tube 3 and will impress a variable positive potential to thegrid of tube 4 during the other fier behaves as a simple half wave rectifier and the voltage applied to the grid of tube 4 is pulsating direct current of radio frequency. Tube 4 amplifies this current and, if the distributed 'capacity of the output transformer 10 is not sumcient for filtering, a suitable capacity 11 may be connected between the plate and cathode of tube 4.

An essential feature of the circuit of Fig. 1 is that the capacity ofone element of the rectifier acts as a load for the other element during each half cycle [The capacity reactance of each element is very much lower than the resistance in the high resistance direction, and

much higher than the resistance in the low re sistance direction. Thus, when two rectifier elements are connected as shown in Fig. 1, during each half cycle one element is-feeding into a load made up of the capacity reactance of the other element, and, since this reactance is many times larger than the resistance of the transmitting element, the current flowing has a very low power factor. Thus enough current to cause the rectifier to operate at its best current can be permitted without placing any great load on the preceding tube or tubes. i

As tube 4 plays no part in the rectification and hence should operate over the linear portion of its characteristic, it is advisable, in order to prevent-overloading of the tube 4 upon reception of signals of relatively large amplitude, to increase the negative bias of thegrid thereof as the signal strengthis increased. Means for automatically so shifting the operating point of this tube are illustrated in Fig. 2 to whichreference should now behad. In Fig.2 means are also included for automatically adjusting the amplification preceding rectification to maintain substantially constant volume of current in the outputcircuit,@ a i In Fig. 2 automatic adjustment of the grid bias of tube 4 is obtained by a resistor 12 in the plate circuit of the tube. One end of resistor 12 is connected to the cathode of tube 4 and the other end of the resistor is connected to the grounded input side of element 1b and, through a second resistor 13 with the negative terminal of the plate battery 7a. Thus the potential difference across resistor 12 due to current flowing through the plate circuit of tube 4 gives a negative bias to the grid of tube 4 increasing with increasing plate current. A capacity 12a across resistor 12 affords a path for any alternating currents.

The potential difference across resistor 13 may be used to increase the negative potential applied to the preceding amplifier, in this instance illustrated as a screen grid tube 3a, with increasing current in the output circuit of tube 4. For this purpose the cathode of tube 3a and the high potential side of resistance 13 are grounded and a conductor 14 is connected between the low potential side of resistance 13 and one end of the secondary of atransformer. 15; the other end of the secondary being connected to the control grid of tube 3a and a capacity 16 being connected between the cathode of tube 3a and the end of the secondary of transformer 15 to whichconductor 14 is attached. Positive potential for the screen grid and plate of tube 3a is indicated as being supplied by a battery 17, the negative terminal of which is connected to the cathode of this tube.

The input to tube 3a is tuned by a variable capacity 18 connected between the control grid and cathode of this tube.

When alternating current is impressed upon transformer 15, it isamplified by tube and transformed to pulsating direct current voltage at the grid of tube 4 by the elements laand lb of the rectifier. Any variation in the amplified current in the plate circuit of tube 4 is then transmitted through transformer 10 to any suitable load circuit connected to terminals 9. Upon an increase in the average plate current of tube 4, the negative bias of the grid of this tube and of the control grid of tube 311 is increased by the potential differences acrossresistors-Q12 and 13 respectively as heretofore described. The increase in negative bias of the grid of tube 4 shifts the operating point of this'tube to prevent overloading thereof and the increase in negative bias of the control grid of tube 3a reduces the effective amplification of this tube to maintain substantially constant output current.

The rectifier elements 1a and lb of Figs. 1 and 2 togetherwith the automatic'grid' biasing resistor 12 of Fig. 2 may be conveniently assembled as shown in Fig. 3' into an adapter for use in coni nection with the usual type of receiving circuit.

In Fig. 3 a portion of a receiving circuit of conventional type, is illustrated as including an input transformer 19 having the secondary thereof tuned by a condenser 20, a five terminaldetector tube socket indicated diagrammatically at 21, 22 23, 24 and 25, a source of potential 26 and a load device 27 which may, for example be any suitable coupling to succeeding amplifiers. Socket element 21 is ordinarily that for the grid lead of a detector tube, socket element 22 for the cathode lead, socket elements 23 and 24 for the heater leads and socket element 25 for the plate lead. Instead, however, of a detector tube, an adapter including the rectifier elements 1a and lb, the resistor 12, short lead wires 28, 29 and 30 and a five terminal socket indicated at 21a, 22a, 23a, 24a and 25a may be inserted in the socket of the receiving circuit and the tube 31 then inserted in the socket of the adapter. The only other change required to transform the conventional receiving circuit into one of the type illustrated in Figs. 1 and 2 is the removal or short circuiting by a conductor 32 of the usual grid condenser and grid leak indicated in dotted lines in Fig. 3. The inclusion of the adapter into the circuit connects the input side of element 111 with the conductor leading to socket element 21, connects one end of resistor 12 and the input side of element 11) with the conductor leading to socket element 22, connects the conductors 28 and 29 with the source of heater current connected to socket elements 23 and 24 and connects conductor 30 with the output conductor connected to socket element 25. The insertion of tube 31 into the socket of the adapter connects the grid of this tube to the output sides of elements 1a and 1b, the cathode to one end of resistor 12, the heater, through conductors 28 and 29, to the source of current therefor and the plate, through conductor 30 with the output circuit.

In the circuits so far described the rectifier elements 1a and 1b have been connected to operate as a half wave rectifier. In Figs. 4 and 5 circuits are illustrated in which these elements are connected for full wave rectification, making possible the elimination of the usual stages of audio frequency amplification, and the feeding of the loud speaker from a single output tube of relatively large capacity. In Fig. 4 the input sides of elements 1a and 1b are connected across the tuning capacity 33 and across the secondary of the input transformer 34; the cathode of the output tube 35 being connected through resistor 12 to the mid-point of the secondary of transformer 34. 7 Tube 35 is indicated as a six element large capacity tube having a cathode grid interposed between the screen grid and plate to shield the screen grid from the secondary electrons emitted by the plate.

output sides of elements 1a and 1b and the plate is connected through the primary of an output transformer 3'7 with the positive terminal of a battery 38, a portion of which also serves as a source of positive potential for the screen grid of tube 35.

In Fig. 5 a three-element large capacity tube 35a is substituted for the tube 35 of Fig.4. EX

cept for the changes in connections introduced by the substitution of this tube the circuits of Figs."

4 and 5 are identical. These changes include the provision of the usual center tapped resistor across the filament of the tube and the connection of the center tap thereof to resistor 12. A capacity 39 corresponding to capacity 11 of Fig. 1 may also be connected between this center tap and the plate of tube 35a if desired. In each circuit the secondary of the transformer 37 may be connected directly to a loud speaker 40 as shown.

With the circuit of either Fig. 4 or Fig. 5, full The control grid of tube 3 5 is connected through an inductor 36 to the" ence across resistor 12 so: astoinsure'operation "of the output tube at the most suitable part of its characteristic.

l/arious circuits embodying'the invention have control grid of 'a'succeeding tube; the cathode of i the tube being suitably connected with the input for either full wave or half wave rectification by said elements'as desired. In-the preferred embodiment of the invention the gridbias of the succeeding tube wasautomatically controlled in response to the output current and this automatic 1 biasing means, together with the rectifier elements, have been shown as conveniently assem- "bled into an adapter for us'ein receivers of conventional design. Obviously various changes could be made'in the circuits disclosed, and features of one circuit could be combined with other features of another circuit without departing from the spirit of the invention. r

The use of the metal oxide rectifier in place of the usual tubedetector not only improves the quality of reception but because of its greater current carrying capacity substantially increases the volume of current transmitted, making it possible, where strong signals are received, to eliminate the usual stage of so-called audio amplification.

The term metal oxide rectifier as used herein and in the appended claims refers to a junction rectifier or an internal boundary rectifier wherein rectification occurs over a substantial area as distinguished from rectifiers of the type of a crystal detector wherein rectification occurs at point contacts only.

The following is claimed:

1. A radio receiving circuit having input and output terminals, 2, tuned circuit connected across the input terminals, a metal oxide rectifier having the input sides of two elements thereof connected to opposite ends of said tuned circuit, a tube having a control grid connected to the output sides of the elements of said rectifier and a cathode connected to the input side of one of said elements and to ground, the output circuit of said tube being connected to the output terminals of the circuit, whereby the rectifier operates as a half wave rectifier and during each half cycle of operation one elment of said rectifier serves as a capacity reactance load for the other element. V

2. A radio receiving circuit according to claim 1 including a resistor in the connection between the cathode of said tube and the grounded input side of one of said elements, the output circuit of said tube including said resistor whereby one element of said rectifier and said resistance co-operate to adjust the negative bias of the control grid of said tube to .preventoverloading thereof.

3. A radio receiving circuit having input and output terminals, a radio frequency amplifier connected across said input terminals, a tuned circuit coupled thereto, a metal oxide rectifier having two elements connected in opposition across said tuned circuit, a tube having a control grid connected intermediate the elements of said rectifier so as to have the voltage applied thereto vary with the direction of current through said tuned circuit, the cathode of said tube being connected to one end of said tuned circuit, means in the output circuit of said tube for varying the negative bias on said radio frequency amplifier in a direction to maintain substantially constant volume of current in the outputcircuit of said tube, and means forcouplingthe output circuit of saidtube to said output terminals. i

4. A radio receiving circuit according to claim 3 whereinmeans connected between the cathode of saidtube and the input side of one of said elements is provided fornegatively biasing the grid with respect to the cathode thereof and for automatically adjusting the negative bias on said tube in accordance witha function of the average plate current to prevent overloading thereof.

-5; An adapter for radio receiving circuits for insertion into the detector tube socket of the circuit comprising in combination? a metal oxide rectifier having two elements connected at their output sides, the input side of one of said elements being adapted for insertion into, a socket element of the detector tube socket, a resistor having one end connected to the input side of the other of the elements of said rectifier andalso being adapted for insertion intofa socket element of the detector tube socket, and a tube socket havingone socket eleinent connected to the other end of said resistor and another socket element connected to the output sides of the elements of said rectifier, said adapter including conductors for connecting in pairs the remaining elements of the socket of the circuit with the remaining elements of the socket of the adapter, whereby when a tube is inserted in the socket of said adapter the circuit will be completed and the tube will operate as an audio frequency amplifier on the output side of the rectifier elements of the adapter.

6. The combination with a radio receiving circuit including a detector tube and a socket therefor of an adapter for insertion into the detector tube socket and including a socket into which the detector tube may be inserted, said adapter including a two element metal oxide rectifier and means for providing a negative bias for the tube when inserted into the adapter socket so as to cause said tube to operate as an audio frequency amplifier on the output side of the rectifier.

7. A radio receiver comprising an audio responsive device, an amplifying tube, a coupling transformer having its secondary connected to said device and its primary included in the plate circuit of said tube, a receiving circuit adapted to receive incoming radio oscillations, a metal oxide rectifier having two elements connected in opposition across the terminals of the receiving circuit, and means for connecting a control grid of said tube intermediate the said elements and the cathode to the receiving circuit, whereby variations in the mean value of the rectified voltages corresponding to modulation are applied to the grid of the tube in such a way that the alternatingcurrent component of this pulsating direct current voltage is amplified and delivered to the audio responsive device through the coupling transformer.

8. A radio receiver comprising an audio responsive device, an amplifying tube, a couplingfz;

transformer having its secondary connected to said device and its primary included inthe plate circuit of said tube, a receiving circuit adapted to receive incoming radio oscillations, a metal oxide rectifier having two elements connected in i.

connecting the cathode to the receiving circuit, whereby variationsin the mean value of the rectified voltages corresponding to -modulation are applied tothe grid of the tube in such away that the alternating current :component of this pulsating direct current voltage is'amplifiedand delivered with substantially-no .distortionto the audio responsive device through the coupling transformer.

19.'A radio receiver -comprising,-an audioresponsive device, an {amplifying tube, a coupling transformer having its secondary connected to said device and its primary includedin the plate circuit of said tube, a receiving transformenra metal oxide rectifier having two elements connected in opposition across the terminals of the secondary of said receiving transformer, and means for connecting a control grid of said tube intermediate the elements of said rectifier and the cathode of said tube intermediate the terminals of the secondary of the receiving transformer, whereby full wave rectification of the received oscillations is accomplished and variations in the mean value of the rectified voltages corresponding to modulation are applied tothe grid in such a way that the alternating current component of this pulsating direct current voltsage Vie-amplified and delivered to the audio responsive device through the coupling transformer.

10. A radio receiver comprising, an audio responsivedevice, an amplifying tube, a coupling transformer having its secondary connected to said device and its primary included in the plate circuit of said tube, a receiving transformer, a

'metaloxide rectifier having two elements conof the rectified voltages corresponding to modulation are applied to thegrid in such a way that the-alternatingcurrent 'component of this pulsating direct current voltage is amplified without overloading the tube and variations corresponding to modulation delivered to the audio responcoupling transformer.

sive device-through the WILLARD P. PLACE. 

